The present application claims the priority of 10 2007 008 375.2-55. The priority document is incorporated by reference in its entirety in the present disclosure.
The subject matter of the invention is an implantable system for determining the accommodation requirement in an artificial accommodation system by optical measurement of the pupil diameter and the surrounding luminance, and the use thereof to restore the accommodative capacity.
The human eye is an optical system which uses a number of refractive interfaces to image focused objects on the retina. In the process, the light waves pass the cornea, the aqueous humor in the anterior chamber of the eye (camera anterior bulbi), the lens (lens crystallina) and the vitreous humor in the posterior segment of eyeball (camera vitrea bulbi), all of which have different refractive indices. If the object distance of the observed object changes, the imaging behavior of the optical system has to change in order to maintain an unchanging focused image on the retina. The human eye implements this by deforming the lens using the ciliary muscle (musculus ciliaris); as a result of this the shape and position of the front and rear sides of the lens basically change (accommodation). In the case of an intact accommodation system in a youthful person, the dioptric power of the system can vary by 14 dpt (breadth of accommodation) between the distance setting (desaccommodated state) and close-up setting (accommodated state). As a result, a youthful person with normal vision (emmetropia) is able to image focused objects on the retina, the objects lying between a far point at infinity and a near point approximately 7 cm in front of the cornea.
Since the ability of the human eye to accommodate reduces with increasing age, a number of artificially implantable lens systems with a variable focus have been developed.
Potentially accommodative intraocular lenses are lenses or lens systems which are inserted in place of the natural lens after the latter has been surgically removed and which are predominantly attached in the capsular bag. Haptics is intended to be applied to axially displace the lens by using a weak residual contraction of the ciliary muscle which is still available.
By way of example, DE 101 55 345 C2, U.S. Pat. No. 6,638,304 B2, WO 03/017873 A1 and U.S. Pat. No. 4,373,218, DE 94 22 429 U1, DE 201 11 320 U1, DE 100 62 218 A1, DE 10139027, WO 02/083033, DE 10125829 A1, US 2004/0181279A1, US2002/0149743, U.S. Pat. No. 6,120,538, U.S. Pat. No. 6,120,538, DE 10155345 C2, U.S. Pat. No. 6,096,078, U.S. Pat. No. 6,638,304, U.S. Pat. No. 6,638,304 and WO004605 all disclose apparatuses for restoring the accommodative capacity.
Furthermore, there are a number of scientific publications relating to the accommodative capacity of lens systems. Reference is made in an exemplary manner to the following publications:
Schneider, H.; Stachs, O.; Guthoff, R.: Evidenzbasierte Betrachtungen zu akkommodativen Kunstlinsen [Evidence-based observations on accommodative artificial lenses], 102. Jahrestagung der Deutschen Ophthalmologischen Gesellschaft [102nd Annual convention of the German Ophthalmological Society] (Berlin, Germany, Sep. 23-26, 2004) (2004)); Kammann, J.; Dornbach, G.: Empirical results regarding accommodative lenses. In: Current Aspects of Human Accomodation. Eds.: Guthoff, R.; Ludwig, K. Kaden Verlag Heidelberg (2001) 163-170, Fine, H.; Packer M.; Hoffmann R.: Technology generates IOL with amplitude of accommodation” (Ophthalmology Times Special Report, Mar. 15, 2005) (2005), Lavin, M.: Multifocal intraocular lenses—part 1. Optometry Today May 2001 (2001) 34-37; Lavin, M.: Multifocal intraocular lenses—part 2. Optometry Today August 2001 (2001) 43-44. Nishi, O.; Nishi, K.; Mano, C.; Ichihara, M.; Honda, T.: Controlling the capsular shape in lens refilling. Archives of Ophthalmology 115(4) (1997) 507-510; Fine, I. H.: The SmartLens—a fabulous new IOL technology. Eye World 7(10) (2002).
Overall, it should be noted that, in principle, the artificial lens implanted during a cataract extraction is unable to focus to different distances. Nor do these operations solve the problem of the human eye no longer being able to sufficiently accommodate to a reading distance of approximately 30 cm once it reaches an age of approximately 45 years. Biological reasons mean that previous attempts of utilizing intraocular structures, in particular the ciliary muscle activity, to mechanically change the refraction of implantable systems have up until now been unsuccessful. Nor is this to be expected in the medium term.
A method of determining the accommodation requirement is to measure the pupil diameter and the surrounding luminance. U.S. Pat. No. 6,638,304 B2 discloses options for measuring the luminance and pupil diameter. In the process, a photosensor measures the luminance, and an electrode which detects changes in the potential of the iris measures the pupil diameter.
Furthermore, so-called pupilometers are known which can measure the pupil diameter optically. Said pupilometers usually emit infrared radiation and detect the reflected light; the pupil diameter can be estimated as a result of this.
However, currently available pupilometers are large and heavy. This means that they are completely unsuitable for being implanted. Furthermore, the image processor for detecting and measuring the pupil requires high computational power.
Using an electrode in the muscle of the iris brings about uncertainties with respect to tissue changes. If the electrode is encapsulated by the tissue, it is no longer possible to measure a sufficient signal. Moreover, this requires additional complexity and a previously unpredictable risk during the implantation.